The present invention relates to a dryer for compressed gas and a compressor installation and a method for drying gas.
Dryers for compressed gas are already known whereby these dryers are provided with a vessel with a drying zone and a regeneration zone therein and if need be a cooling zone; an inlet to the drying zone for the supply of compressed gas to be dried and an outlet from the drying zone for the removal of dried gas; an inlet to the regeneration zone for the supply of a hot regeneration gas and an outlet from the regeneration zone; a rotatable drum in the vessel with a regeneratable drying agent therein; drive means for rotating the aforementioned drum such that the drying agent is successively moved through the drying zone and regeneration zone, whereby the aforementioned outlet of the regeneration zone and any cooling zone is connected to the aforementioned inlet of the drying zone by means of a connecting pipe with a cooler and condensate separator therein, and whereby these dryers are configured such that, during the operation of the dryer, the gas flow rate that leaves the regeneration zone via the outlet of the regeneration zone is equal or practically equal to the gas flow rate that is then guided into the drying zone via the inlet in order to be dried.
An example of a dryer whereby the flow rate of regeneration gas leaving the regeneration zone matches the flow rate of gas to be dried that is guided into the drying zone is described in EP 2.332.631. The hot compressed gas is first guided through the regeneration zone where it acts as a regeneration gas and absorbs moisture from the drying agent for the regeneration of this drying agent. In the embodiments described in EP 2.332.631 environmental air is compressed for example, by means of an air compressor for example, whereby during compression this air not only undergoes a pressure increase, but also experiences a temperature increase such that the relative humidity of this air falls and this air is able to absorb moisture from the drying agent. Dryers that make use of the heat of compression present in the compressed regeneration gas are known in the industry by the name of ‘heat of compression’ dryers or HOC dryers.
After passing through the regeneration zone the hot regeneration gas presents a higher relative humidity. The moist gas that leaves the regeneration zone is then guided through a cooler in the connecting pipe such that the temperature of this gas falls below the pressure dew point and condensation of the moisture present in this gas occurs. The droplets hereby formed are then removed by means of the condensate separator such that the now cooled, compressed gas is 100% saturated and is fully guided to the inlet of the drying zone and through this drying zone, where the drying agent extracts moisture from this compressed gas by means of sorption (adsorption and/or absorption).
The dried gas that leaves the drying zone can be used in a compressed air network located downstream from the dryer for all types of purposes such as for pneumatic conveyors, the drive of pneumatically driven tools and similar.
It is characteristic of the type of dryer described above in EP 2.332.631 that the entire or practically entire compressed gas flow, originating from the compressor, is first guided through the regeneration zone and then guided in full through the drying zone. Dryers that make use of such a full flow of the gas through the regeneration zone and drying zone are also called full-flow dryers.
In the connecting pipe between the outlet of the regeneration zone and the inlet of the drying zone there is a blower to increase the pressure of the gas flow in order to ensure that the pressure at the outlet of the drying zone is higher than the pressure at the inlet of the regeneration zone, such that it prevents moist gas from the compressor being able to leak to the outlet of the drying zone, where it could mix with the dried gas, such that the gas that goes downstream to the consumer network via the dryer output would be much less dry.
EP 2.332.631 also describes a variant in which an intermediate cooling zone is provided between the regeneration zone and drying zone that follows the regeneration zone in the direction of rotation of the drum, whereby cool dry air is tapped off at the outlet of the dryer and guided through the cooling zone to the outlet of the regeneration zone.
In other arrangements, for example as described in WO 00/74819, the bulk of the hot compressed gas that leaves the compressor is first guided through an aftercooler to then be transported to the drying zone. Only a part of the hot compressed gas is tapped off downstream from the compressor and upstream from the aftercooler to be transported to the regeneration zone for the regeneration of the drying agent. Such a dryer as described in WO 00/74819 is thus a heat of compression dryer, but does not operate according to the full flow principle, as not all the flow of hot compressed gas is used as regeneration gas.
A heat of compression dryer is also described in WO 2011/017782 that does not operate according to the aforementioned full flow principle. The dryer as described in WO 2011/017782 presents the special characteristic that the regeneration zone comprises two subzones, i.e. a first subzone through which a first regeneration flow is transported and an intermediate zone or second subzone through which a second regeneration flow is transported and whereby the dryer is configured such that the relative humidity of the aforementioned second regeneration flow is lower than the relative humidity of the aforementioned first regeneration flow that is guided through the first subzone. The second subzone is preferably at the end of the regeneration zone. In this way more moisture can be absorbed from the drying agent than in a conventional way, such that more moisture can be absorbed from the gas to be dried in the drying zone by the drying agent.
With such a dryer according to WO 2011/017782 it can happen that in certain circumstances, for example when starting up a compressor that supplies a gas to be dried to the dryer, the desired flow of the second regeneration flow cannot be realised as the pressure in the drying zone has not yet built up sufficiently. In some cases gas could even temporarily go from the regeneration zone, through any leaks or even via the tap-off pipe, into the outlet of the drying zone, which could result in undesired dew point peaks. The present invention is aimed at avoiding such circumstances as much as possible.